The southern Appalachian orogen preserves a complex distribution of metamorphism and deformation varying in timing, magnitude, and spatial extent. These complexities give rise to disparate interpretations for southern Appalachian tectonic evolution, which complicates the testing and interpretation of tectonic models in this system. New monazite (Mnz) and xenotime (Xtm) laser ablation split stream (LASS) analyses alongside Mnz-Xtm thermometry in the orogenic core in the eastern Blue Ridge (EBR), western Inner Piedmont (WIP), and Cat Square terranes (CST) of North Carolina yield new constraints that define distinct pro- and retrograde metamorphic events. The EBR preserves two prograde thermal events: the Taconic (similar to 470-440 Ma, >660 degrees C) and Neoacadian (similar to 380-340 Ma, 600-700 degrees C), separated by a period of cooling (exhumation?) and followed by garnet breakdown from 339 to 329 Ma. Evidence of pervasive Neoacadian ductile deformation in the EBR is largely limited to the Brevard fault zone (BFZ), indicating that a major rheological gradient existed across the BFZ during the Neoacadian and early Alleghanian. Southeast of the BFZ, in the WIP and CST, monazite data define a protracted Neoacadian evolution from early mineral growth at similar to 405 Ma at similar to 450-600 degrees C to >700 degrees C at similar to 360 Ma, followed by early Alleghanian retrograde metamorphism and deformation (<345 Ma, 350-500 degrees C). These constraints, together with previously reported thermobarometric data, define a P-T-t evolution for the WIP and CST consistent with Neoacadian crustal flow, while the coeval presence of a thermal-rheological boundary along the BFZ further supports a model of Neoacadian crustal "escape" flow within the orogen.

The Grenville orogen lacks a foreland basin along nearly its entire exposed length in North America, precluding examination of orogenic evolution recorded in foreland basin sediments. New U-Pb detrital zircon geochronology is presented for the late Mesoproterozoic Hazel and Lanoria Formations (West Texas), purported Grenvillian foreland clastic sequences, with new U-Pb zircon crystallization ages for magmatic rocks that overlie and intrude the Lanoria and constrain its depositional age. These new data permit comparisons with the Middle Run Formation, the only other known Grenvillian foreland sequence (US midcontinent subsurface), and other late Grenvillian clastic sequences across Laurentia. The Lanoria Formation (quartz arenite and feldspathic arenite) is overlain by Thunderbird rhyolite (1117 +/- 8Ma [2 sigma]) and intruded by Red Bluff Granite (1109 +/- 8 Ma). The Hazel Formation (eolian litharenite-fluvial conglomerate redbed sequence) was deposited on a 1260-1240 Ma volcanic-sedimentary sequence (Allamoore and Tumbledown Formations) and contains clasts of those units. The Hazel and underlying formations were interfolded within the Grenville Front Tectonic Zone footwall at ca. 1035 Ma. The Lanoria Formation is dominated by ages correlated with central Laurentian (1510-1360, 1800-1600 Ma) and eastern Laurentian Grenvillian (1280-1120 Ma) basement age provinces, with minor Archean ages (2900-2500 Ma). The Hazel Formation is dominated by central Laurentian Proterozoic and Archean basement ages, proximal sources within the exhuming Grenville orogen (1380-1320, 1280-1230 Ma), and ca. 1100 Ma ages correlated with the southwest Laurentia large igneous province, which was emplaced into central Laurentian terranes. The Lanoria is thus dominated by distal cratonic and eastern Laurentian orogenic input. The Hazel contains a mix of proximal syn-orogenic and distal cratonic input. Age constraints require that the Lanoria and Hazel Formations are not time-correlative, paired distal-proximal facies of a Grenvillian foreland basin, as was previously proposed. The Hazel Formation is lithologically identical to the Middle Run Formation and was deposited during a similar syn- to late Grenvillian time span. This is consistent with the presence of a foreland basin receiving cratonic and orogenic sediment input extending along the US midcontinent region during the Grenvillian orogeny.

Southwest Amazonia is proposed to have collided with southeast Laurentia during the Grenville orogeny. In Laurentia, the collision produced a continental-scale late Mesoproterozoic to early Neoproterozoic clastic wedge dominated by detrital zircon (DZ) sourced from Grenvillian magmatic rocks (major Geon 11 and 10, with minor Geon 13, 12, and 9 ages: the "Great Grenvillian Sedimentation Episode"). New DZ ages in clastic units from southwestern Brazil permit testing the hypothesis that Grenvillian sediment from southeast Laurentia spilled onto western Amazonia during Rodinian assembly. Late Mesoproterozoic arenites are dominated by Geons 18, 17, 15, 14, and 13 ages sourced from Amazonia basement provinces. Two samples exhibit major Geon 12 and 11 ages with minor Geon 18-13 ages. Geon 12 and 11 correspond to a conspicuous age gap in Amazonian magmatic events. Latest Neoproterozoic samples exhibit minor Geon 13 to 9 ages interpreted to be sourced from the Rondonia-San Ignacio or Sunsas provinces of western Amazonia. Late Neoproterozoic and Devonian age spectra exhibit multiple Amazonian age modes 2500 to 500 Ma but with no dominant modes. The age distributions for all samples indicate a lack of Laurentian Grenville sediment influx to southwest Amazonia during Rodinian assembly and breakup. The enigmatic Geon 12 ages are interpreted to corre-spond to a buried Andean source or the southwestern Grenville province in Laurentia. In contrast to exposed basement in southwestern Amazonia, Andean basement clastic sequences and Pleistocene to Recent Amazon River sediments exhibit Grenville dominance of DZ ages, strikingly similar to eastern Laurentia clastic systems. The Andean Grenville dominance may be accounted for by extensive Grenvillian crust beneath the Andean clastic wedge containing a major component of Geons 12, 11 and 10 magmatic rocks, and which was not being fully exhumed until the Neoproterozoic, similar to Laurentian Grenville.(c) 2022 Published by Elsevier B.V. on behalf of International Association for Gondwana Research.

ABSTRACT Lithic and quartz arenites of the Central Appalachian Basin deposited by late Paleozoic Laurentian fluvial systems are widely interpreted to be sourced by recycling of late Precambrian and early Paleozoic clastic sequences in the Appalachian Orogen. U-Pb and (U-Th)/He age distributions for detrital-zircon and Th-Pb age distributions for detrital-monazite, detrital-zircon and monazite textures (including detrital diagenetic monazite, which prove recycling), sandstone petrology, heavy-mineral abundances, and other detrital proxies are all accounted for by the following: 1) lithic arenite is directly sourced from late Neoproterozoic metasediments in the proximal Appalachian fold and thrust belt via transverse drainages, 2) the late Neoproterozoic sediments were recycled from early Neoproterozoic, post-Grenvillian clastic sequences, 3) Cambrian quartz arenites along the Laurentian margin were recycled from Neoproterozoic sequences with local cratonic input, 4) although dominated by sediment of ultimate Grenvillian age, quartz arenites require ∼ 40% of Paleoproterozoic and Archean input, interpreted to be recycled from late Neoproterozoic to Devonian clastic sequences of the northern Appalachians and/or southern (Scottish–Irish) Caledonides in the distal reaches of a longitudinal drainage system. Ordovician to Mississippian clastic sequences and their metamorphosed equivalents in the Appalachian crystalline core were also likely sediment sources. Quartz arenite does not result from mixing of lithic arenite with other sources because of differences in textural and compositional maturity, and in heavy-mineral characteristics. Input from the Laurentian craton, commonly cited as the source for Paleoproterozoic and Archean detrital zircon in the eastern Laurentian clastic systems, is untenable here because of: 1) the presence of Paleozoic monazite derived from Appalachian Neoproterozoic and early Paleozoic metasediments, 2) abundant detrital chromite, and 3) abundant Paleozoic detrital muscovite. Multiple recycling explains all observed sedimentologic and mineralogic characteristics of the two lithic types. Incorporation of published detrital-zircon data for Paleozoic to modern clastic sequences in eastern Laurentia reveals that Grenville-age zircons experienced at least five and potentially ten recycling events since entering the clastic system in the Neoproterozoic. Recycling also explains the abundance of quartz pebbles in conglomerates of the quartz-arenite lithofacies, and the range of detrital-muscovite 40Ar/39Ar ages in quartz arenites of the Appalachian Basin.

ABSTRACT Glaciogenic rocks are rare in the Appalachian area and occur only locally as parts of Upper Precambrian and Upper Devonian successions. This trip examines a relatively recent exposure of Upper Devonian glaciogenic diamictites and laminites along Corridor H (U.S. Highway 48) in east-central West Virginia, USA. The diamictites occur in the Rockwell Member of the Price Formation, in transition with the underlying redbeds of the Upper Devonian Hampshire Formation. Palynology indicates that all parts of the Rockwell Member exposed at the locality are present in the Retispora lepidophyta – Verrucosisporites nitidus (LN) Miospore Biozone and are, therefore, of Late Devonian, but not latest Devonian, age. This biozone occurrence indicates correlation with parts of the Oswayo Member of the Price Formation, the Finzel tongue of the Rockwell Formation, and with dropstone-bearing parts of the Cleveland Shale Member of the Ohio Shale in northeastern Kentucky. Much previous work supports a glaciogenic origin for the diamictites and associated sediments, which occur as parts of a shallow-marine incursion that ended the Hampshire/Catskill alluvial-plain/deltaic complex across much of the Central Appalachian area. The glaciogenic succession is part of nearshore, marginal-marine strata that accumulated in an embayment during the Cleveland-Oswayo-Finzel transgression, which represents a global eustatic sea-level rise and foreland subsidence related to Acadian/Neoacadian deformational loading in the adjacent orogen. Detrital-zircon-provenance data from the diamictites indicate Ordovician plutonic sources as well as reworked Neoproterozoic to Ordovician sedimentary sources that can only have been derived from nearby Inner Piedmont sources like the Potomac terrane. This provenance suggests that Acadian/Neoacadian convergence of the exotic Carolina terrane with the New York and Virginia promontories along the southeastern margin of Laurussia not only uplifted Inner Piedmont source areas into a high mountain range capable of supporting glaciation in a subtropical setting, but also, through deformational loading, enhanced regional subsidence and the incursion of shallow seas that allowed alpine glaciers access to the open sea.

ABSTRACT The Mesoproterozoic southeastern margin of Laurentia, which consisted primarily of the ca. 1.5–1.35 Ga Granite-Rhyolite Province, was extensively reworked during ca. 1.3–0.9 Ga phases of the Grenville orogenic cycle. Questions remain for much of southeastern Laurentia regarding the transition from the Granite-Rhyolite Province to Grenville orogenic cycle, and for potential collisional interaction with Amazonia, due to Paleozoic sedimentary cover or tectonic reworking. Basement rocks sampled by drill core in the east-central United States include 1.5–1.35 Ga magmatic rocks, some overprinted by late Geon 10 (Ottawan) orogenesis, which are the most outboard evidence of Granite-Rhyolite Province crust. Newly recognized 1.35–1.30 Ga (pre-Elzevirian) granitic orthogneisses within the Mars Hill terrane of southeastern Laurentia (1) expand the along-strike distribution of the earliest crustal age components of the Grenville orogenic cycle in Appalachian basement inliers; (2) contain Geon 19–16 inherited zircons; and (3) were metamorphosed during late Ottawan to Rigolet tectonism. Paragneisses enveloping the Geon 13 orthogneisses are dominated by Geon 19–16 and Geon 13–12 detrital zircons overgrown by Geon 10–9 metamorphic zircon. The zircon age systematics require the paragneiss protoliths to be younger than orthogneiss protoliths and be partly sourced from the latter. Orthogneisses and paragneisses have Pb isotope compositions that overlap those of south-central Appalachian and southwest Amazonia basement, both of which are distinct from Laurentian Pb isotope compositions. The boundary between Amazonian (southern Appalachian) and Laurentian (northern Appalachian) Pb isotope compositions is thus a terrane boundary, with Geon 13 magmatic rocks being the youngest common crustal component. In comparison, the Paraguá block of the southwestern margin of Amazonia consists of a Geon 19–16 basement complex intruded by the batholithic-scale Geon 13 San Ignacio granite suite. The latter also contains inherited Geon 19–16 zircon and has Pb isotope compositions that help define the Amazonian trend. The correspondence of magmatic, inherited, and detrital ages and similarity in Pb isotope compositions are consistent with an origin for the exotic/orphaned Mars Hill terrane as an outboard sliver of the Paraguá block that developed before Grenvillian orogenesis (Geons 12–9). Manifestations of the latter are concentrated around the margins of the Paraguá block in the Sunsás (southwest), Nova Brasilândia (north), and Aguapeí belts (east). The Sunsás belt is a mostly low-grade metasedimentary belt with only minor Geon 10–9 magmatism and no Geon 12 or 11 magmatism, thus distinguishing it from the Mars Hill terrane. The Arequipa-Antofalla terrane, exposed in Andes basement inliers, lies outboard of the Sunsás belt and has Pb isotope and geochronologic characteristics that permit a correlation with the Mars Hill terrane and a paleogeographic position between the Mars Hill terrane and the Sunsás belt. The histories of the Mars Hill terrane, Arequipa-Antofalla terrane, and Paraguá block merge during Geons 10–9 and final collisional orogenesis between southeast Laurentia and southwestern Amazonia.

The common-Pb isotope composition (207Pb/204Pb vs. 206Pb/204Pb) of detrital K-feldspar was measured on the same clastic units from southeastern Laurentia that were previously characterized by detrital zircon and detrital monazite geochronology for provenance analysis. The purpose is to test a model that invokes late Paleozoic recycling of sediment initially sourced from erosion of exhuming Grenvillian basement in the Neoproterozoic. The approach takes advantage of the difference in Pb isotope compositions between Laurentian and Amazonian cratonic sources documented by previous workers. Neoproterozoic samples sourced from southern Amazonia and central Laurentian basement that serve as controls on methodology plot within Pb isotope space characteristic of their respective sources. K-feldspar in the Cryogenian Ocoee Supergroup in the southern Appalachian orogen falls within the field of Pb isotope compositions defined by south-central Appalachian basement (SCAB). The latter, in turn, exhibits Pb isotope compositions characteristic of Amazonia, because SCAB was transferred to Laurentia from Amazonia during Rodinian assembly. In contrast, K-feldspar in early Cambrian arenite falls within the Laurentian field, indicating a shift in the early Paleozoic to a sediment source from the Laurentian Craton. K-feldspar in Lower Pennsylvanian lithic arenites of the Central Appalachian Basin exhibit Pb isotope compositions that fall within the SCAB field but at higher Pb isotope ratios than in the inferred Ocoee sources. Incorporation of all provenance constraints requires an immediate source that is isotopically more radiogenic than the Ocoee but similar in all other petrologic and geochronologic characteristics, for example, other Cryogenian to Ediacaran units along strike in the Appalachian orogen. The results further demonstrate the importance of having multiple detrital mineral proxies for accurate provenance analysis rather than using detrital zircon geochronology alone.

The tectonometamorphic evolution of the southern Appalachians, which results from multiple Paleozoic orogenies (Taconic, Neoacadian, and Alleghanian), has lacked a consensus interpretation regarding its thermal‐metamorphic history. The Blue Ridge terranes have remained the focus of the debate, with the interpreted timing of regional Barrovian metamorphism and associated deformation ranging from early (Taconic) to late Paleozoic (Alleghanian). New monazite U‐Pb geochronology and thermobarometric data are integrated with previously reported geo‐ and thermochronology to delimit the Paleozoic thermal‐metamorphic evolution of these terranes. Monazite compositional, textural, and U‐Pb age systematics are remarkably consistent for all samples, yielding a single dominant age mode for each sample. The western, central, and eastern Blue Ridge terranes yield weighted mean monazite U‐Pb ages of 450–441, 459–457, and 458–453 Ma, respectively. Thermodynamic modeling using mineral assemblages yields peak conditions of 600°C–650°C and 5.8–8.9 kbar for staurolite and kyanite grade western Blue Ridge units, including the stratigraphically youngest unit in the Murphy syncline, which also yields a weighted mean monazite U‐Pb age of 441 Ma. The Taconic metamorphic core of the central Blue Ridge yields peak conditions of 775°C and ∼11.5 kbar. Combined, these ages indicate that the relatively intact Barrovian metamorphic progression mapped across the Blue Ridge of Tennessee, North Carolina, and northern Georgia is solely of Ordovician (Taconic) age. Synthesis of this new data with existing geo‐ and thermochronology support a model of Barrovian metamorphism resulting from construction of a Taconic accretionary wedge and subduction complex, followed by post‐Taconic unroofing during Neoacadian and Alleghanian thrusting.

Analytical methods for Zircon U-Pb and monazite Th-Pb SIMS geochronology, zircon U-Pb LA-ICP-MS geochronology; data tables and supporting previous work.